Adding _optional_ counting for operations with numbers

NOTE: in order to enable this feature please define HAVE_NUMSTATS in your own <BUILD_DIR>/libpolys/misc/auxiliary.h or by adding "CPPFLAGS=-DHAVE_NUMSTATS" to configure call

add: will count cancelations, e.g. zero results of addion (extra counter: n_CancelOut)
add: Interface: NumberStatsInit - sets all counters to zero, NumberStatsPrint - prints all non-zero counters (named by the interface method) (via LIB"schreyer.lib"; which will load "syzextra.so")
chg: also cleanup and wrapping lately added methods (e.g. CoeffsName/String)

NOTE: there plenty "unwrapped" other calls to internal coeff. functions (e.g/ in slimgb implementation) - a separate pull request will be produced for them.